1. Field of the Invention
The present invention relates to a temperature abnormality detecting structure for a fluid pipe, which detects an occurrence location of an abnormality in a pipeline or piping for transporting and flowing various types of fluids, e.g., a low-temperature fluid such as a liquefied natural gas (LNG) and a high-temperature fluid such as a high-temperature vapor, on the basis of a temperature abnormality.
2. Description of the Related Art
In a pipeline for transporting a fluid, e.g., a liquefied natural gas, if the fluid flowing through the pipeline is blown out of the pipeline due to cracking of a transporting pipe, damage or destruction of the pipe, and the like, it may lead to a disastrous accident. The same applies to a piping in a plant or factory which transports a fluid, e.g., various types of chemical products and chemicals, various types of gases, and a high-temperature vapor. In a heat exchange facility, e.g., a heating piping of a building and the like, leakage of a high-temperature heating medium from a pipe may cause a decrease in heating efficiency, in heat exchange efficiency, and the like, although it may not cause a disastrous accident. Therefore, in a fluid pipe as described above, when leakage or outflow of a fluid flowing in the fluid pipe occurs, it is required to immediately detect the location of the leakage or outflow, so that repair and the like of the portion where the leakage or outflow occurs can be quickly performed.
A pipe such as fluid transporting and flowing pipeline and piping as described above transports and often flows therethrough a fluid having a predetermined temperature difference from atmospheric temperature. In such a pipe, the leakage and outflow of the fluid flowing from the pipe to the outside of the path can be detected by detecting the temperature near the pipe. For example, in an LNG transporting pipeline, since the LNG itself has a very low temperature, if the LNG in the pipe leaks or flows to the outside of the pipe due to cracking in the pipe and the like, the temperature near the portion where the leakage or outflow occurs is rapidly decreased. Hence, the occurrence location of the leakage of the LNG can be detected by constantly monitoring the temperature distribution of the pipe in the longitudinal direction. Inversely, in a piping of a high-temperature heating medium, e.g., a high-temperature vapor, since a temperature increase occurs near the portion where the leakage occurs, the occurrence location of the leakage of the high temperature heating medium can be detected by constantly monitoring the temperature distribution of the pipe in the longitudinal direction.
As a sensor capable of monitoring the temperature distribution of a pipe in the longitudinal direction, a Raman scattering optical fiber distribution type temperature sensor is known. An example of a system in which this distribution type temperature sensor is used for detecting an occurrence location of a ground-fault in an electric power cable line is a system disclosed in Published Unexamined Japanese Patent Application No. 1-267428.
A principle of measuring a temperature distribution by the above-described Raman scattering optical fiber distribution type temperature sensor is as below. When light is incident into an optical fiber, the light is scattered due to the small fluctuation of a refractive index in the optical fiber, absorption, or re-emission of light by molecules, atoms of the optical fiber. There are as the scattered light Rayleigh scattering light having the same wavelength as the incident light and Raman scattering light having a different wavelength from the incident light. The latter Raman scattering light is generated by the thermal vibration of molecules, atoms of the optical fiber, and its intensity depends largely upon its temperature. Therefore, when pulse light (normally a laser pulse) having a specific wavelength is used as the incident light, the delay of a period of time until the light is returned as the scattered light and the intensity of the Raman backscattering light are detected, whereby the temperatures of the positions of the optical fiber in the respective directions can be measured. Therefore, when an optical fiber as the temperature detector of the Raman scattering optical fiber distribution type temperature sensor is laid along the pipe of the pipeline or piping as described above, and when the fluid flowing in the pipe leaks or flows to the outside of the pipe due to cracking, damage, and destruction of the pipe, an abnormal temperature outside the pipe is detected, thereby obtaining the abnormality occurrence location.
To perform maintenance and supervision of a pipe, e.g., a pipeline, it is rare to achieve maintenance and supervision of the entire pipeline of a long distance by the same maintenance duty office and person in charge. It is general to divide the pipe of the pipeline into a plurality of maintenance sections and perform maintenance and supervision of the respective sections by different maintenance duty offices and persons in charge. In this case, regarding maintenance and supervision of the pipe, e.g., a pipeline, it is necessary to know which maintenance section the occurrence location of the temperature abnormality belongs to. Particularly, in the vicinity of the boundary between the maintenance sections, it is often necessary to know where a temperature abnormality occurs in the adjacent maintenance sections.
In a piping in a factory or building, a piping for flowing a high-temperature vapor, a heating medium, or the like is often provided to a plurality of rooms through the walls between the rooms. In this case, it is necessary to know in which room the temperature abnormality occurs. Especially, in the vicinity of a wall as the boundary of rooms, it is often necessary to precisely know in which room the temperature abnormality occurs.
According to the Raman scattering optical fiber distribution type temperature sensor as described above, it is possible to detect a temperature distribution of the optical fiber in the longitudinal direction. However, as a matter of fact, its distribution resolution, especially its detecting accuracy of the occurrence location of a temperature abnormality is not very high. Therefore, if the optical fiber of such a temperature sensor is merely laid along the pipe, it is very difficult to precisely detect, in the vicinity of a maintenance section boundary of a pipeline as described above, in which section a temperature abnormality occurs, or to precisely detect, in a piping provided to a plurality of rooms as described above, which room the temperature abnormality location belongs to in the vicinity of a boundary between adjacent rooms.